LDH-Based Voltammetric Sensors

Abstract

Layered double hydroxides (LDHs), also named hydrotalcite-like compounds, are anionic clays with a lamellar structure which have been extensively used in the last two decades as electrode modifiers for the design of electrochemical sensors. These materials can be classified into LDHs containing or not containing redox-active centers. In the former case, a transition metal cation undergoing a reversible redox reaction within a proper potential window is present in the layers, and, therefore, it can act as electron transfer mediator, and electrocatalyze the oxidation of an analyte for which the required overpotential is too high. In the latter case, a negatively charged species acting as a redox mediator can be introduced into the interlayer spaces after exchanging the anion coming from the synthesis, and, again, the material can display electrocatalytic properties. Alternatively, due to the large specific surface area of LDHs, molecules with electroactivity can be adsorbed on their surface. In this review, the most significant electroanalytical applications of LDHs as electrode modifiers for the development of voltammetric sensors are presented, grouping them based on the two types of materials.

Keywords: anion exchangeability; electrocatalysis; layered double hydroxides; modified electrodes; voltammetric sensors.

Figure 1

DPVs of Ni/Co LDH/SPE in 0.1 MPBS (pH 7.0) with various concentrations of sumatriptan (a–l: 1.0, 7.5, 15.0, 45.0, 75.0, 100.0, 150.0, 200.0, 250.0, 300.0, 350.0, and 400.0 µM) and naproxen (a–l: 1.0, 10.0, 20.0, 45.0, 75.0, 100.0, 125.0, 175.0, 225.0, 325.0, 350.0, and 400.0 µM). Insets: (A) the plot of peak current versus sumatriptan concentration, and (B) the plot of peak current versus naproxen concentration. Reproduced from ref. [23] (open access).

Figure 2

CV scans of different electrodes in 0.1 M phosphate-buffered solution (pH 7.0) in the absence (a, b) and presence (a′, b′) of 2.0 mM H₂O₂. Scan rate: 0.1 V∙s⁻¹. Reproduced with permission from ref. [27].

Figure 3

FESEM images at high magnifications of (A) LDH/GCE and (B) AgND/LDH/GCE. (C) CVs of 0.5 mmol L⁻¹ PZA at bare GCE (a), LDH/GCE (b), AgND/GCE (c), and AgND/LDH/GCE (d). Supporting electrolyte: 0.1 M PBS (pH 7.0). Reproduced with permission from ref. [5].

Figure 4

Inkjet-printed carbonaceous electrodes (CNT (a) and graphene (b)) before and after a potentiodynamic deposition of Ni/Al LDH. (c) Calibration graph for methanol in 0.1 M KOH using a Ni/Al LDH/inkjet-printed CNT electrode. (d) CVs for the determination of ethanol in 0.1 M KOH using a Ni/Al LDH/inkjet-printed graphene electrode. Unpublished results for discussion.

Figure 5

Proposed reaction mechanism of UA and BPA at the surface of modified MWCNT paste electrode. Reproduced with permission from ref. [34].

Figure 6

DPV responses of the Cu/Al LDH/CFYM/GPGE in PBS (pH 7.0) solution at a scan rate of 10 mV s⁻¹ with different concentrations of DCF from (a) to (l) are 1.99, 3.98, 5.96, 7.94, 9.9, 11.86, 13.81, 15.74, 17.68, 19.61, 21.53, and 23.44 mM. The inset shows the relationship of current responses to DCF concentration. Reproduced with permission from ref. [43].